The iliopsoas muscle group consists of two muscles: the psoas muscle and the iliac muscle. These muscles work together to help the hip flex. The psoas muscle connects to the lumbar vertebrae L1 through L5. The other end of the psoas muscle connects to the tendon on femur bone. The lumbar plexus, a nerve bundle that originates at the middle of the spine, supplies the psoas with nerves. The iliac muscle connects to the ilium, the largest bone of the pelvis, on the top and runs under the psoas to the same tendons of the femur bone as the psoas muscle. The nerves of the iliac muscle are supplied by the femoral nerve, which is located in the leg.
At the very least, the tension and/or spasm in muscles that cross over the hip and attach onto the pelvis can contribute to imbalance, in terms of how strong and flexible each muscle group is in relation to the others. But muscle imbalance in the hips and the spine may make for pain, limitation and/or posture problems. It can also increase the healing challenge put to you by an existing injury or condition, for example, scoliosis.
It’s a common issue, says Prevention advisor Rob Danoff, director of family and emergency medicine residency programs at Aria Health in Philadelphia. "For people who sit a long time at work, the hip flexors and rotators become tight, and the gluteal muscles become weak," he says. "This combination negatively affects our ability to walk, maintain proper posture, and the stability of our spine."
The hip flexors are a group of five muscles that connect the femur (or thigh bone) to the pelvis. They move in one of two ways. When the pelvis is stationary, a contraction of the hip flexors will draw the femur upward—think the classic "goose step." Conversely, if the femur is stationary, a contraction of the hip flexors will tilt the pelvis forward and the butt back—think of the pull-back portion of Garth's many hip thrusts beginning at about 40 seconds in ... foxy lady!
Holland also suggests doing strength work in different planes of motion to keep all the muscles in and around your hip flexors, especially your glutes, firing correctly.“You can’t have good hip flexion if your glutes are tight or weak,” Nurse says, “so it’s super important that you’re always stretching and strengthening the front of your hip flexor and the back, which are the glute muscles.”

Now doing the same thing over and over again and somehow getting a different response may seem like a good idea to some, whereas others may think they just need to “spend more time” with their hip flexor stretches to force that tight and unforgiving muscle to finally loosen up. But the simple fact of the matter is that if it’s not working, it’s probably not the right solution.

Unfortunately hip mobility issues like these are some of the most common problems I see in the weightlifting population. However, the issues manifest differently in different people. In some, it's a basic inability to descend below parallel—or anywhere near it—in squat variations. In others, it can contribute directly to debilitating lower back pain, even in people who spend hours every week strengthening their backs.
How to: Lie on your back with your right knee bent and foot flat on the floor (a). Extend your left leg up to the ceiling and wrap a strap around the sole of your left foot (b). While holding both ends with your left hand, extend your right arm directly out to the side in order to anchor yourself (c). Slowly let the left leg fall toward the left while keeping your right side grounded. Hold for six to eight breaths, then repeat on the opposite side.